180 



SUBMAEINE CABLE LAYING AND EEPAIEING. 



C and D, and line and earth to the exposed terminals A and B. 

 These connections being made, the signalling current enters 

 from the line at A, passes through four coils to C, where it 



Fig. 91. — Lodge LightniDg Guard. (Double Pattern.) 



goes through the instrument to D, and returns by the other 

 four coils to earth at B. It will be seen that between the 

 opposite pairs of coils sparking points are fixed which offer dis- 

 charging paths in shunt. 



Lightning entering by 

 the line at A will more 

 readily jump across the 

 gap to B than take the 

 path by the coils and the 

 receiving instrument, be- 

 cause the self-induction of 

 the coils chokes back any 

 sudden rush of current. 

 If the whole discharge is 

 not taken between A and 

 B there are four other 

 pairs of points for the flash 

 to expend its energy before 

 affecting the instrument, 

 so that the instrument 

 connected to C D is at 

 the protected end. When 

 used at a cable-house the 



terminals A B are connected to the cable conductor and sheath 

 respectively, and the terminals C D to the two land-line leads. 

 In the single pattern (Fig. 92) there are three terminal?, A, B 



Fig. 92. — Lodge Lightning Guard. 

 (Single Pattern.) 



